|Publication number||US7962605 B2|
|Application number||US 09/989,474|
|Publication date||Jun 14, 2011|
|Priority date||Nov 20, 2001|
|Also published as||US20030097425|
|Publication number||09989474, 989474, US 7962605 B2, US 7962605B2, US-B2-7962605, US7962605 B2, US7962605B2|
|Original Assignee||Microsoft Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (15), Non-Patent Citations (4), Referenced by (6), Classifications (17), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention generally relates to the area of computer systems. More particularly, the present invention concerns distributed networks, and methods and systems for discovering resources (e.g. devices) in distributed networks.
As computer network technology matures, enterprise-wide networks are evolving from simple, isolated local area networks into complex distributed networks. Today's larger enterprise-wide networks include hundreds of nodes comprising computers and network devices capable of carrying out a variety of tasks. Examples of network nodes include personal computers (workstations) running application software, printers, scanners, facsimile machines, plotters, file servers, external network communication interfaces, etc.
The increased number of nodes within enterprise-wide networks, as well as the increased breadth of configuration information maintained for such nodes, raises a need to automate network device/node discovery. Device discovery involves populating resource information tables with information defining particular attached devices. Such information can include by way of example: location (e.g., the TCP/IP network address/port of the resource, the HTTP URL, etc.), model/manufacturer name, protocols supported, configurations (for example, resource model, command set, network protocol, and memory size), and operational statuses (e.g., good, poor, or malfunction). Such discovery facilitates advertising resource locations (addresses) to requesting clients, configuring nodes for network communication, and managing the nodes' operation. Automated network device discovery facilitates discovering network resources and storing such information in a manner that enables client nodes to search for and gain access to shared resources in potentially very large enterprise-wide networks.
In many instances enterprise-wide networks are divided into subnets. Such networks are divided into subnets for a variety of reasons. One reason is cost. Enterprise-wide networks in many instances are spread over large geographic regions—even across multiple continents. From a cost perspective, it is impractical to maintain a permanent, fully functional link between nodes located across such large distances. Networks comprising multiple subnets temporarily enable communication between nodes on distinct subnets by activating bridges that link the two subnets on an as needed basis.
Another reason to divide a network into subnets is performance. Long-distance wide area network links generally support substantially lower bandwidth than local area networks. Furthermore, request conflicts and increased sharing of available bandwidth can lead to unacceptable communication delays as more communicating nodes are added to a network link. In the case of a link that allows asynchronous transmission requests, the likelihood of colliding requests increases. Even in cases where collision avoidance techniques are used, for example when each node is assigned a particular time slot in which to request access to the link to complete a transmission, the effective transfer rate can become unacceptably low when too many requestors are present. Thus, in cases where a large number of nodes communicate with one another relatively frequently, each communicating node on the shared link is allocated substantially less bandwidth than is generally needed by the nodes.
However, the above problems associated with very large, non-segmented networks can be addressed in many instances by creating subnets. Dividing a large network into subnets raises penetrable barriers between the groups of nodes that make up each of the subnets. Communications from a first node addressed to a second node within a subnet generally are not passed outside the subnet within which the communications originate. In order to pass outside the subnet a sending node generates a message with an address that references another subnet. Such barriers achieve reductions in unnecessary transmissions outside the network. However, such barriers inhibit device discovery over a network. The degree to which the subnet barriers can inhibit or unduly complicate device discovery outside a subnet is addressed herein below with reference to known discovery methods.
Resources connected to a network may comply with differing communication protocols. Examples of such protocols include Transport Control Protocol over Internet Protocol (TCP/IP), or Universal Plug and Play (UPnP). Moreover, the resources may associate with disparate operating systems. For example, a networked printer may be associated with a printer server that operates Windows NT in one subnet, whereas a networked scanner may be associated with another printer server that operates Linux in another subnet. In some cases network device vendors provide means for facilitating discovery of their devices that are independent of the devices' operating system environments.
An exemplary enterprise-wide distributed network links multiple subnets together. Each subnet is associated with security principle, which determines groups of users who have access to the subnet. Different subnets are associated with separate security principles. Thus, a client in a subnet may not be allowed to discover a resource in a subnet that has a different security principle. Furthermore, a subnet may reside in a remote geographical location that cannot be reached by a multicast message. Consequently, a client in one subnet may not be able to search resources in a remote subnet, even though the two subnets have the same security principle.
A number of network device discovery methods are utilized in networks. Service Location Protocol (SLP) is an IETF standard that provides a scalable framework for automatic resource discovery on Internet Protocol networks. It bases its discovery mechanism on service attributes, which are essentially different ways of describing a service.
Universal Plug and Play (UPnP) is an evolving architecture developed by MICROSOFT to extend an original MICROSOFT Plug and Play peripheral model to a network environment including many network devices supplied by different vendors. UPnP operates primarily at low level network protocol layers, for example, the TCP/IP layer. UPnP uses a Simple Service Discover Protocol (SSDP) to discover services on Internet Protocol based networks.
The present invention comprises a method and system for discovering resources in a network having multiple subnets. Discovery agents are employed on a subnet to identify resources, and in particular embodiments devices (e.g., printers), that are accessible to other nodes within a network. Simple discovery agents (SDAs) perform a set of operations facilitating sharing resource discovery information, provided by discovery agents within a subnet, with requesting nodes throughout a network. Such sharing of network resource data facilitates dynamic discovery of devices outside a subnet.
Since subnets support multiple SDAs, steps are taken to reduce the number of SDAs that respond to inter-subnet requests for identification of network resources. A selection process establishes an active simple discovery agent (ASDA) that responds to requests to identify instances of a network resource (e.g., a printer) within a particular subnet. ASDAs also propagate the resource identification requests to neighboring ASDAs, thereby enabling a resource (e.g., device) discovery request to reach the subnets of a network that contain at least one ASDA via an ASDA mesh linking the neighboring subnets.
In an embodiment of the invention, the ASDAs establish an ASDA mesh over the network via queries to neighboring subnets. A requesting ASDA transmits multicast queries on adjacent subnets seeking identification of ASDAs on those subnets. The ASDAs on the adjacent subnets issue responses advertising their network addresses and ASDA status. The returned addresses are stored by the requesting ASDA.
ASDAs are the designated inter-subnet resource discovery actors for the subnets with which they are associated. Thus, if a resource identification request designates the particular subnet, then the ASDA provides a response identifying relevant resources (e.g., printers) to the requester (e.g., a print server that originated the request). Otherwise, a receiving ASDA forwards the request to adjacent ASDAs based upon their previous responses, but does not issue a response to the original requester.
While the appended claims set forth the features of the present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which:
In accordance with an exemplary embodiment of the invention described herein below simple discovery agents are executed upon nodes within subnets of an enterprise network. An active simple discovery agent (ASDA) is established in each of the subnets of the network. Each ASDA discovers ASDAs residing on other subnets within the network and maintains a list of the discovered ASDAs. An ASDA searches for ASDAs and requested resources within the network by searching for ASDAs on adjacent networks and propagating received ASDA search requests to ASDAs on adjacent subnets. In a particular embodiment of the invention, a directory service maintains a record of the ASDA lists.
The present invention facilitates discovering resources, such as printers, in a distributed network having multiple subnets when such resources are not located upon a same subnet as a requestor. Such instances arise for example when a user in a first subnet at a remote office seeks to print a document at a printer located at an enterprise's main office located some distance from the remote office. In that case, a print server at the remote office passes the request from the remote subnet to a printer located at the main office subnet. However, in order to complete such a transmission, the remote print server generally provides an address for the main office printer.
Before describing particular ones of the figures, a number of general definitions are provided for terms that are used extensively herein below. Terms are generally described through examples and descriptions of general functionality. It is noted that such definitions are primarily intended to render illustrative exampled of the present invention.
The term “resource” as used herein includes a variety of network nodes. Such network nodes include printers, workstations, servers (for example, printer servers or file servers), scanners, services, programs, hardware, etc. The resources communicate over the network via communication protocols such as, for example, TCP/IP.
An SDA (simple discovery agent) executes upon a subnet node and, using one or more discovery protocols, renders a set of resources presently located on the subnet. Locally, subnets implement resource discovery protocols, for example, UPnP or simple-location-protocol (SLP). A search for resources within a subnet is performed according to any of many known and available discovery/search protocols. It is noted that the present invention does not, in its broadest sense, require discovery of local (subnet) resources according to any particular discovery protocol. The present invention instead concerns how locally discovered resources are discovered by resource users located upon different subnets.
An ASDA is a specially designated SDA, established in each subnet, for discovering other ASDAs on other subnets of a network. The discovery process, by way of example includes ASDA search requests passed to neighboring subnets. A network directory service stores information comprising resource discovery information regarding the ASDAs in the network.
Although not required, in an embodiment of the present invention a computer implements the above-summarized functionality by executing instructions, such as program modules. Generally, program modules include routines, objects, components, data structures and the like that facilitate performing particular tasks or implementing particular abstract data types. The term “program” includes one or more program modules.
The invention is capable of being carried out on a variety of conventional and unconventional computing machine types including: cell phones, personal computers (PCs), hand-held devices, multi-processor systems, microprocessor-based programmable consumer electronics, network PCs, minicomputers, mainframe computers and the like.
With reference to
Device 100 may also contain one or more communications connections 112 that allow the device to communicate with other devices. Communications connections 112 are an example of communication media. Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. As discussed above, the term computer readable media as used herein includes both storage media and communication media.
Device 100 may also have one or more input devices 114 such as keyboard, mouse, pen, voice-input device, touch input device, etc. One or more output devices 116 such as a display, speakers, printer, etc. may also be included. All these devices are well known in the art and need not be discussed at greater length here.
Each of the subnets 210, 220, 230 and 240 comprises a locally linked set of resources. For example, subnet 210 includes resource 211, resource 212, and resource 213. Subnet 220 includes resource 221 and resource 222. Subnet 230 includes resource 231 and resource 232. Subnet 240 includes resource 241 and resource 242. A particular example of a resource is a network printer. However, as mentioned previously herein above, the term resources in the context of the present invention encompasses a variety of network devices. Within each subnet, device discovery agents (DDAs) execute known local and network device discovery protocols.
In the example depicted in
With specific reference to
In each subnet, an ASDA is selected from the multiple identified SDAs of the subnet. Though a subnet conceivably includes multiple ASDAs, such redundancy is not necessary or particularly desirable. The ASDA on each subnet is responsible for maintaining identification information for ASDAs in other subnets within the network and maintaining a list of addresses of the discovered ASDAs for purposes of creating a resource discovery mesh across the entire enterprise network. In a particular embodiment of the invention, each ASDA is responsible for maintaining a list of the ASDAs within adjacent (neighboring) subnets. The extent of each ASDAs discovery of other ASDAs (such as its ability to pass discovery requests through subnets that do not have an ASDA) is modulated by a time-to-live (TTL) value in requests to neighboring subnets for identification of their ASDAs. Thus, in the case of large networks each ASDA maintains only a subset of the entire set of ASDAs within a network. However, in the event that access to a complete set of ASDAs is required, a network-wide set of ASDA addresses is maintained within a directory service 290 and replicated over multiple subnets within the enterprise network.
With continued reference to
The ASDAs within each of the subnets communicate with the directory service 290 to store at least the ASDA identity information of the type maintained by the ASDAs within the network depicted in
To successfully locate a resource (or resources) in a target subnet, the ASDA in the same subnet as an originator of the request determines the identity/address of the ASDAs in the neighboring subnets, and then ASDA passes the request to the neighboring ASDAs. The recipients, in turn pass the received request until the request has propagated to at least the ASDA in the target subnet. The ASDA in the target subnet issues a response to the originator of the request including the requested resource information.
Utilizing the above-described mesh comprising neighboring ASDAs in a network, a resource discovery request propagates through the network via the mesh until the request is received by an ASDA associated with the target subnet. The target ASDA determines whether a requested resource is available on the target subnet. The target ASDA thereafter issues a response to the issuer of the resource discovery request.
To ensure proper operation of an ASDA in each subnet, any one of multiple SDAs in a subnet are capable of operating as the ASDA for the subnet. To avoid excessive, redundant communications it is preferable to only have a single ASDA at any time for a subnet. The selection of an ASDA is accomplished by either manual assignment or automatic selection according to an automated selection procedure. Such selection is discussed herein with reference to
In an exemplary enterprise network environment, security properties, which are referred to herein as trusted domains are utilized to establish potential candidates for ASDA status. In particular, SDAs that are trusted within the subnet are considered for appointment to ASDA status. Furthermore, trust relationships can also be extended to access by ASDAs to neighboring ASDAs.
In an embodiment of the invention such as the one depicted
After establishing the ASDA communication mesh capability described above, the ASDAs propagate resource (e.g., printer) discovery requests received from nodes within their subnets to the ASDAs on the neighboring subnets. For example, ASDA 213 receives a request from resource 211 (e.g., a print server) of subnet 210, for discovery of all printers on subnet 240. The ASDA 213 propagates the request (including the network address of the requesting resource 211) via a unicast message to ASDAs 221, 231 and 241 on neighboring subnets 220, 230 and 240. The ASDAs 221 and 231 pass the request on to any neighboring subnets other than the source of the request (which do not happen to exist in this particular illustrative network configuration). Since ASDAs 221 and 231 do not reside on the identified subnet (240), they do not issue a response to the resource 211. The ASDA 241 however, recognizes the request as being directed to its subnet 240, and the ASDA 241 issues a response to the requesting resource 211's address including discovery information that it presently possesses with regard to any printers on subnet 240.
The device discovery agents 302 obtain information from devices within the network and publish that information into a device discovery database 316. The device discovery information stored within a device discovery database 316 structure is available to (or maintained by) all SDAs. In an embodiment of the invention, the device discovery database 316 is sub-divided according to the device discovery agent protocols that are utilized to obtain the information for devices within the subnet. Though not depicted in the drawings, an embodiment of the invention includes device discovery agent management (DDM). The DDM facilitates installing and removing particular device discovery agents in the set of device discovery agents 302 and registers their existence on a device discovery information container. The DDM creates the subdirectory in the device discovery database 316 corresponding to a newly installed device discovery agent on a computing machine.
The present invention addresses sharing the above-described “local” device discovery information, rendered by local discovery agents within a subnet, with requestors located anywhere in a network. This capability is provided in a scalable and reliable manner by simple discovery agents (SDAs) such as an SDA 318 depicted in
Within a network comprising multiple subnets, the SDA 318 carries out an inter-subnet device discovery information sharing method described herein. This method includes establishing the identities of active SDAs (ASDAs) within adjacent subnets, and then passing received inter-subnet device discovery requests to the identified ASDAs on the adjacent subnets. The addresses of the neighboring ASDAs are maintained in an ASDA list 319 (described herein below with reference to an exemplary format depicted in
In the particular example set forth in
Turning now to
Furthermore, an active ASDA (e.g., ASDA 213 a) multicasts the WHO_IS_ASDA message 501 to each of the neighboring subnets (e.g., subnet 220) to obtain the identity of the neighboring ASDAs (e.g., ASDA 221 a) and facilitate the creation of an ASDA mesh across the multiple subnets within the network. The ASDAs within the neighboring subnets each unicast the ASDA_AD message 502 back to the originating ASDA (e.g., ASDA 213 a) thereby declaring each responding SDA entity as the ASDA for the identified subnet. The ASDA_AD messages 502 from the neighboring ASDAs are used by the originating ASDA to build its ASDA list illustratively depicted in
An SDA_WILLING message 503 is multicast by any SDA on a subnet. The SDA_WILLING message 503 is transmitted during bidding stage for selecting an ASDA among potentially several available SDAs on a subnet. The SDA_WILLING message 503 indicates that the issuer of the message seeks to compete with other SDAs on a subnet for ASDA status.
A SEARCH_DEVICE message 504 is a unicast message that initiates a search for a device, or more generally a resource. The SEARCH_DEVICE message 504 is issued by a requesting resource (e.g., a print server) to either an ASDA on the resource's subnet or a directory service. A resource on a subnet unicasts the SEARCH_DEVICE message 504 to the ASDA on its subnet and initiate a search for a resource. An example of such a request is to find all printers on a network. In response, the ASDA on the subnet unicasts the SEARCH_DEVICE message 504 to each of the ASDAs on neighboring subnets. By repeating the request message at receiving ASDAs, the SEARCH_DEVICE message 504 is propagated on an ASDA mesh throughout the network.
Rather than search for a device or resource via the ASDA the ASDA mesh, a requesting resource issues a SEARCH_DEVICE message 504 to a known directory service address. The directory service is located on the subnet or alternatively on another subnet within the network.
If a recipient of a SEARCH_DEVICE message 504 has responsive device/resource information, the recipient issues a FOUND_DEVICE message 505. In an embodiment of the invention, the FOUND_DEVICE message 505 is unicast to the originating device/resource. For example, if the requester is a print server on a first subnet, then all responses from ASDAs or the directory service are unicast directly back to the requesting print server.
Turning briefly to
The port number 512 identifies the port of a recipient to which a received data packet should be forwarded. In general, a port number is associated with a program or a process running on a networked machine. By way of example, the SDA on an ASDA is assigned a particular port number (e.g., 1800). The port number can also be used to specify a particular function to be performed by a message recipient. However, in an embodiment of the invention, parameters identifying a particular request/function are passed in the other data field 513. The other data field 513 is also utilized to pass back requested information about discovered devices. As mentioned previously herein above, the other data field in a request message holds the network address of the originator of the discovery request (e.g., a print server).
A set of administrative messages are provided the administer to the ASDA mesh and maintain its healthy state of operation. A set of administrative messages is provided, by way of example, in
An ASDA, once selected, issues messages to interested parties on a subnet or network (a neighboring ASDA) informing them of its presence. A HEARTBEAT REQ message 553 is issued by an ASDA to its neighboring ASDAs to ensure that they are operating properly. A HEARTBEAT RESP message 554 informs the requesting ASDAs that the recipient of a previous HEARTBEAT REQ message 553 is indeed operational.
When an ASDA shuts down on its own, it informs neighboring ASDAs to ensure that they do not issue further requests until a replacement ASDA advertises itself. A SHUTDOWN REQ message 555 informs the neighboring ASDAs of the issuer's shut down. Recipients respond via a SHUTDOWN RESP message 556 acknowledging receipt of an instance of the SHUTDOWN REQ message 555.
When an entity requests device discovery information, it may thereafter monitor progress by issuing a PROGRESS REQ 575. A corresponding PROGRESS RESP 576 provides a level of completion value to the requester.
One of the primary functions performed by ASDAs is to provide requestors with device discovery information. A SEARCH DEVICE REQ 577 and its corresponding response message SEARCH DEVICE RESP 578 initiate a searching operation. An ASDAs response informs the sender that the ASDA: is interested, discarded the request, or the request was redundant.
A REMOVE REQUEST REQ 579 and its corresponding REMOVE REQUEST RESP 580 enable a requester to withdraw any previous request to an SDA.
A NEW DEVICE REQ 581 message and its corresponding NEW DEVICE RESP 582 facilitate adding a new entity that is to be notified in association with an identified request.
A FOUND DEVICE REQ 583 and FOUND RESOURCE RESP 584 are the messaging mechanisms for ASDAs to notify requesters of devices/resources located in response to a device discovery request. This request/response pair follows the SEARCH DEVICE REQ/RESP 575/576 that initiates a search for devices on an ASDAs subnet.
In an embodiment of the invention, SDA capability is incorporated into multiple nodes on a subnet. However, only one of the SDA-ready nodes is needed to create a network-wide mesh, and therefore only one SDA is selected in a subnet as the active SDA (ASDA). In some instances, the selection of an ASDA is accomplished by an automated election process from the willing SDAs in a subnet according to an automated election procedure. The various states of operation of a subnet with regard to ASDA election are illustrated, by way of example, in
At state 630 an ASDA election algorithm is carried out wherein the SDAx issues an SDA_WILLING multicast message on the subnet and competes with other willing SDAs on the subnet for ASDA status. The election of an ASDA is made through a comparison of the willing SDAs operation status and properties. The election criteria include, for example, physical memory size, CPU speed, operating system version, and computation capacity. If the SDAx is not elected as the ASDA at state 630, then SDAx transitions from the election state 630 to the idle state 620. If the SDAx is selected as the ASDA, then SDAx transitions from election state 630 to an ASDA status declaration state 640.
At state 640 the SDAx issues an SDA_AD message thereby declaring its ASDA status. From state 640 the SDAx can transition to a shutdown state 650 wherein it notifies other interested network entities that it is shutting down, and upon completion of shutdown procedures passes to End state 660. Otherwise, the SDAx transitions from state 640 to the election state in response to an appropriate event, such as receiving an SDA_WILLING notification from a better SDA within the subnet.
Alternatively, following step 612 the SDAx receives an SDA_WILLING message 503 is received at step 613 b. The SDA_WILLING message indicates that another SDA intends to compete for ASDA status. Next, at step 615 the ASDx determines whether the SDA is better than the SDA that sent the received SDA_WILLING message. If the SDAx determines that it is better, then ASDx enters the election state 630. Otherwise if the SDAx is not better, then it enters the idle state 620.
The third option encountered from step 612 is that no ASDA_AD signal is received during the timeout period. In that case, the SDAx notes a timeout at step 613 c and responds by entering the election state 630.
Alternatively, if an ASDA_AD message is received at step 622 b, then the SDAx merely resets the timer and continues to wait for a next message at step 621. Finally, the timer can time out without the SDAx receiving either of the two above-mentioned messages being received. The SDAx notes the timeout at step 622 c and enters the election state 630.
If no response received in the REFRESH_INTERVAL, the SDAx notes the timeout at step 635 a and returns to step 632. If at step 634 the ELECTION_INTERVAL expires, then at step 635 b the SDAx notes the timeout and control passes to step 638. At step 638 the SDAx determines whether it is the best candidate for ASDA status based upon the established election criteria. If the SDAx is the best candidate, then the SDAx enters the ASDA status declaration state 640. If the SDAx is not better than one of the other willing SDAs, then control passes to step 632.
Will waiting at step 634, if an ASDA_AD message is received at step 635 c, then at step 636 the SDAx determines whether it is better than the SDA that sent the SDA_AD message. If the SDAx is indeed better, then control passes from step 636 back to step 632. Otherwise, the SDAx passes from step 636 to the idle state 620.
Finally, if while waiting at step 634, the SDAx receives an SDA_WILLING message at step 635 d, then control passes to step 637. At step 637, the SDAx determines whether the SDAs is better than the SDA that sent the SDA_WILLING message. If the SDAx is indeed better, then control passes to step 634 (in effect disregarding the SDA that sent the SDA_WILLING message). If at step 637 the SDAx determines that it is not better than the sender of the SDA_WILLING message, then control passes to step 639. At step 639 the SDAx resets the ELECTION_INTERVAL timer and returns to wait step 634.
However, if the SDAx receives an ASDA_AD message at step 643 c while executing the wait period at step 642, then the SDAx enters the election state 630 described herein above. Finally, if the SDAx receives an SDA_WILLING message at step 643 d while waiting at step 642, then control passes to step 644 wherein the SDAx determines whether it is better than the sender of the SDA_WILLING message. If the SDAx is indeed better, then control returns to step 641. Otherwise, if the SDAx is not better, then SDAx passes from the declaration state 640 to the election state 630.
Having described the general operation of a system embodying the present invention and exemplary states of SDAs in such a system, attention is directed to a particular exemplary embodiment of the present invention involving network printer discovery. With reference to
A number of ASDAs, printers and print servers are distributed throughout the network 700. Subnet 701 contains a printer server 712, a printer 714, a printer server 713, and an ASDA 711. Subnet 702 includes ASDA 722 and printer 721. Subnet 703 includes printer 731 and ASDA 732. Subnet 704 includes ASDA 741. Subnet 705 has printer server 751 that is also the ASDA for the subnet 705. For exemplary purposes, all the subnets have the same security properties and are in the same trusted domain.
In an embodiment of the invention, SDA software is executed upon multiple nodes within each subnet including the depicted network printers 714, 721, 731; printer servers 712, 713, and 751; and networked computers 711, 722, 732, and 741. In each subnet, an ASDA is selected from among the available SDAs according to the states and steps illustratively depicted, by way of example, in
In an embodiment of the invention, a printer server in an originating subnet requests discovery of all printers throughout the network 700. Such discovery is initiated by the print server sending a device (printer) discovery request to the ASDA in its subnet. The recipient ASDA identifies its neighboring ASDAs in subnets adjacent to the originating subnet and forwards the request to the neighboring ASDAs. In response to the forwarded request, the ASDAs discover printers in their respective subnets, and if printers are present, then the ASDAs pass the discovery results to the requesting printer server. In addition to responding to the printer server the neighboring ASDAs propagate the discovery request to neighboring ASDAs in a discovery process that continues until the discovery request has propagated throughout the network.
There is a potential for an ASDA to receive multiple request messages, and execute multiple searches/responses, associated with a same initial device discovery request. However, an embodiment of the invention seeks to reduce such redundancy. By way of example, globally unique identifiers that accompany resource (e.g., device) discovery requests enable the ASDAs to recognize, and therefore ignore, redundant discovery requests for which the ASDAs have previously executed a search and issued (if appropriate) a response. Furthermore, in an embodiment of the invention, an ASDA does not propagate an identified discovery request to a neighboring ASDA from which it has previously received the identified discovery request. Each of these network traffic/redundancy controls is present in the example provided herein below wherein a printer server issues a network-wide printer discovery request.
At step 804, ASDA 711 searches its list of printers on subnet 701 that results in discovery of printer 714. At step 805, ASDA 711 unicasts a FOUND_DEVICE message to printer server 712. The FOUND_DEVICE message comprises a parameter specifying the network location of printer 714. An exemplary parameter states: //subnet 701 address/printer 714 address/.
The ASDA 711 next propagates the printer discovery request onto neighboring subnets. However, in an exemplary embodiment of the present invention, before the ASDA 711 requests identification of resources, it determines the neighboring ASDAs at step 806 by issuing a multicast WHO_IS_ASDA message on subnet 702, which is adjacent to subnet 701. In response, at step 807, ASDA 722 unicasts an ASDA_AD message to ASDA 711 claiming that it is the ASDA in subnet 702. At step 808, ASDA 711 propagates the SEARCH_DEVICE request, that originated from printer server 712, to ASDA 722, thereby requesting ASDA 722 to identify all printers on subnet 702 to the printer server 712. After initially determining that ASDA 722 has not previously responded to the uniquely identified discovery request, at step 809 the ASDA 722 searches its printer discovery databases for subnet 702. This search results in identification of printer 721. At step 810, the ASDA 722 unicasts a FOUND_DEVICE message to printer server 712. The message identifies the location of printer 721 in subnet 702 of the network.
As part of its network printer discovery request propagation function, at step 811 the ASDA 722 multicasts a WHO_IS_ASDA message to all neighboring subnets (e.g., subnet 701, subnet 703, and subnet 704) that are adjacent to subnet 702. In response, at step 812, ASDA 711, ASDA 732, and ASDA 741 separately unicast ASDA_AD messages to ASDA 722 claiming they are ASDAs for their respective subnets. At step 813, ASDA 2 forwards the SEARCH_DEVICE message to ASDA 732 and ASDA 741 for searching printers in their respective subnets. However, ASDA 722, recognizes the GUID of the request as corresponding to a prior request provided by the ASDA 711 and does not forward the message to ASDA 711. In an alternative embodiment, the ASDA 722 transmits the discovery request to all neighboring ASDAs regardless of whether the ASDA 722 previously received the identified request from one or more of the neighboring ASDAs.
As will be explained further herein below, it is possible for an ASDA to receive a discovery request that it has previously executed. There are a variety ways that an ASDA can respond to redundant discovery requests. In alternative embodiments of the invention, recipients of redundant requests (from two or more independent ASDAs) respond to the redundant requests by issuing a discovery response or ignoring the request altogether. In an embodiment of the invention, if an ASDA previously propagated a discovery request, then the ASDA does not propagate the request if received again.
In response to receiving the SEARCH_DEVICE message, at step 814 ASDA 732 and ASDA 741 search their subnet device lists for printers. At step 815, ASDA 732 unicasts a FOUND_DEVICE message to the printer server 712. The message sent by the ASDA 732 identifies the network location of the printer 731. In the illustrative embodiment of the invention, since there are no printers on the subnet 704 the ASDA 741 does not issue a response message to the printer server 712. Alternatively, the ASDA 741 issues a null response to the printer server 712 indicating that there are no discoverable printers on the subnet 704.
At step 816, ASDA 732 multicasts a WHO_IS_ASDA message to subnet 702 and subnet 704. At step 817, ASDA 722 and ASDA 741 unicast ASDA_AD messages to ASDA 732 claiming that they are the ASDAs in subnet 702 and subnet 704, respectively. At step 818, ASDA 732 utilizes the returned ASDA addresses from step 817 to unicast a SEARCH_DEVICE message to ASDA 741 requesting searching printers in subnet 704. ASDA 732, recognizes the GUID of the request as corresponding to a prior request provided by the ASDA 722 and does not forward the message to ASDA 722. At step 819, ASDA 741 further recognizes the GUID of the request from the ASDA 732 as one that it has previously executed and therefore does not search for available network printers on its subnet. Alternatively, the ASDA 741 searches for network printers, and finds none (see, step 814). Furthermore, in the alternative exemplary embodiment the ASDA 741 unicasts a FOUND_DEVICE message to the printer server 712 that indicates that there are no network printers on the subnet 704 (or no message at all).
In continuation of the request propagation, at step 820 the ASDA 741 multicasts a WHO_IS_ASDA message on subnet 702, subnet 703, and subnet 705. At step 821 ASDA 722, ASDA 732, and ASDA 751 unicast ASDA_AD messages to the ASDA 741 declaring their ASDA status. At step 822, ASDA 741 forwards the SEARCH_DEVICE message to ASDA 751 requesting identification of network printers on subnet 705. The ASDA_AD messages from ASDA 722 and ASDA 732 are noted, but the SEARCH_DEVICE message is not sent to those two ASDAs since they previously sent the identified printer discovery request to the ASDA 741. At step 823 ASDA 751 searches for discovered network printers on subnet 705. Since no printers are present on subnet 705, the ASDA 751 does not issue any response to the printer server 712.
During step 824, ASDA 751 multicasts a WHO_IS_ASDA request on subnet 704. In response, at step 825 the ASDA 741 unicasts an ASDA_AD message to the ASDA 751. Since ASDA 751 previously received the current printer discovery request from the ASDA 741, ASDA 751 does not propagate the printer discovery request.
Having described an exemplary network printer discovery method it is noted that the present invention contemplates a number of variations to the exemplary steps. Such modifications include the order of execution of the depicted steps. In addition to the potential for multiple request recipients to simultaneously propagate a resource (e.g., printer) discovery request over the network, a number of other variations to the depicted steps are contemplated in executing a network-wide search for resources (e.g., printers). It is not necessary for an ASDA to receive a search request before looking for devices or obtaining the addresses of neighboring ASDAs. Such discovery (including discovery of devices/resources on a subnet) can occur at any time. However, by waiting until receiving a request to discover neighboring ASDAs, an ASDA ensures that it will have proper neighboring ASDA addresses when it unicasts a discovery search request. Having particular designated ASDAs in subnets reduces the amount of communications generated when network-wide device discovery is invoked. Furthermore, the search request to neighboring nodes can alternatively comprise a multicast message—that is responded to only by the current ASDA on a receiving subnet. Whether an ASDA (1) sends a request to a previous sender of an identified discovery request, (2) responds to redundant requests, and (3) issues a response to a requester even when the requested device is not present on a subnet, are implementation choices altered in various embodiments of distributed device discovery methods and systems embodying the present invention.
It will be appreciated by those skilled in the art that a new and useful method and system for discovering networked resources in distributed networks have been described herein. In view of the many possible embodiments to which the principles of this invention may be applied, however, it should be recognized that the embodiments described herein with respect to the drawing figures are meant to be illustrative and should not be taken as limiting the scope of invention.
Those skilled in the art to which the present invention applies will recognize that the illustrated embodiments can be modified in arrangement and detail without departing from the spirit of the invention. For example, the invention is described as installing a SDA in multiple node types on a subnet. However, other configurations may also be employed. For example, a network printer may not have an SDA installed therein. Although the invention is described in terms of software modules or components, those skilled in the art will recognize that such may be equivalently replaced by hardware components. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof.
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|U.S. Classification||709/224, 709/220|
|International Classification||H04L29/08, G06F15/173, H04L29/12, H04L29/06, G06F15/177|
|Cooperative Classification||H04L67/10, H04L29/12207, H04L29/06, H04L61/20, H04L29/12009|
|European Classification||H04L29/12A3, H04L29/12A, H04L29/08N9, H04L29/06, H04L61/20|
|Feb 27, 2002||AS||Assignment|
Owner name: MICROSOFT CORPORATION, WASHINGTON
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Effective date: 20020205
|Nov 24, 2014||FPAY||Fee payment|
Year of fee payment: 4
|Dec 9, 2014||AS||Assignment|
Owner name: MICROSOFT TECHNOLOGY LICENSING, LLC, WASHINGTON
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:MICROSOFT CORPORATION;REEL/FRAME:034541/0001
Effective date: 20141014